Generally a flash welder comprises a sturdy metal base on which are mounted a stationary platen and a moveable platen (as suggested in FIG. 1) the moveable platen being guided for sliding movement toward and away from the stationary platen.
Each platen has a clamp thereon in which work pieces W1 and W2 are respectively clamped. The usual flash welder also includes a welding transformer having a primary P and a secondary S. The primary is connected to a power controller C which in turn is connected to a source of electrical energy. Opposite ends of the secondary are electrically connected to respective clamps.
The workpieces to be welded together are loaded into respective clamps so that adjoining ends are slightly spaced and the clamps are firmly engaged on the workpieces. The moveable platen is thereafter driven by a hydraulic cylinder H in a direction toward the moveable platen while transformer secondary current is caused to flow between the workpieces to cause an arcing or flashing between the workpieces. The arcing or flashing removes any irregularities between adjoining ends of the workpieces and causes a heating and softening of such ends.
After a predetermined amount of flashing, the forward movement of the moveable platen is increased materially (in some cases five to ten times the speed of flashing motion). This is termed the upset motion of the moveable platen and causes the heated workpiece surfaces to be forced together, thereby lowering electrical resistance between the workpieces and simultaneously increasing current flow (upset current) therebetween. This abrupt increase in motion may be effected by the flow of high pressure hydraulic fluid through larger conduits Co and to cylinder H. A solenoid controlled valve V may be interposed in the larger conduits to permit or prevent flow of upset fluid therebetween. Current to the coil of the solenoid of the valve is controlled by switch contacts Sw which are controlled in a manner to be described in connection with the description of the preferred embodiment of any invention.
My invention provides an electrical circuit which will initiate the start of upset of a flash welding machine at an operator-selectable value of flashing energy. This electrical circuit, by means of a simple adjustment of electrical switch means, may include a few additional electrical components to enable initiation of the start of upset, or termination of upset, as a function of platen position rather than as a function of flashing energy, thus providing the machine operator a choice of upset control.
Further, by simple adjustment of additional electrical switch means, further electrical components may be included to control the distance the moveable platen moves during the upset portion of the welding cycle independent of platen position at the start of upset. Also, a meter may be included in the circuit to display either upset distance or upset initiation position depending upon the setting of an electrical switch.